I would definitely swich his litter to something more rabbit friendly, if you haven’t already. As you’ve read, pine and corn cob are both unhealthy for your bun. Carefresh, Yesterday’s News, Feline Pine, or even wooden stove pellets that aren’t treated with an accelerant are all much better options. You could also try shaking out his hay before you give it to him, sometimes hay dust can get up a bun’s nose and make him sneeze. Also, any scented products (carpet powders, scented candles) are really bad for your rabbit, too. Even though you may not use carpet powder in the bunny’s room, it definitely stays in the vacuum. (My roommate uses nasty rose carpet powder that makes both Warren and I sneeze – I just air out my room very well when I use it).
However, he may be sick. Check the insides of his front paws/legs, to see if there are any crusties there. Also, keep an eye on his nose, and eyes, to see if they are watering. It is possible for your rabbit to have allergies, but just as possible for him to be sick. If something doesn’t seem right, call your vet at the least, before starting him on any meds. If your vet wants to see him, see if there are any payment plans or such for the visit your vet may be able to work out.
Good luck, and I hope your little guy’s feeling better soon!